Microwave antennas are well known, and are commonly used in satellite and radar systems for communications purposes.
Radar antenna designs are well known. A single simple antenna tends toward being omnidirectional and, as a consequence, it cannot be focused in one direction. However, if several antennas are combined into an array, it is possible to shape the energy being transmitted into a more focused beam, which allows directional transmission from point to point and is useful for communication relay stations. If an antenna array has more antenna components, a narrower beam can be produced because each component is fed with an Rf signal which is split several times, such that each component has the same phase. This produces a maxima emanating from the center of the array, in which the signals are in-phase and are additive. The energy emanating to the side of the array is minimized because of the destructive interference which is due to the energy from each of the components being generally out of phase; the phase deviation is a consequence of the geometric array variables.
In a phase shifting antenna array, the phase of the antenna components can be adjusted to be controllably different. It is then possible to shift the maxima energy to an angle pointing in a desired direction, as is known conventionally for scanning array. In this way, it is possible to steer or scan the direction of the electromagnetic energy emanating from the antenna array electronically, without physically moving the antenna. Scanning antennas enable programmable directed communication in a single direction at a time, in which the beam is focused in the desired direction, and are also used in direction finding radar, and for imaging of the environment.
There are many types of scanning antennas. One such antenna uses a mechanical steering mechanism. However, the physical mass of a mechanically steered antenna is large and permits only low speed scanning, which is not fast enough for many direction finding applications.
Electrical scanning arrays are known, which function using phase shifting principles. One type of electrical scanning array is a ferrite scanning array, which operates by adjusting the applied magnetic field causing changes in signal delay. While this method enables fast scanning, it is expensive, its design is too complex to be efficiently mass produced and it is bulky. Thus, the phase shifting component requires as much space as the entire patch array.
Another type of electronic scanning uses PIN switches, which cause a phase delay by switching between different feed line lengths. This system is capable of fast scanning. However, PIN switches cannot handle the high power common in such antenna transmission and are susceptible to overload damage.
Another known method for electronic scanning uses ferroelectric materials which change signal delay when an electric voltage is applied to the material. However, no practical design has yet been produced for a scanning array using ferroelectric material. The potential benefits of the ferroelectric technology include much smaller size, simpler assembly, and large cost benefits. Unlike the ferrite phase shifter, ferroelectric phase shifters only consume 10% of the antenna array's area.
Existing scanning arrays using ferroelectric phase shifters and antenna patches employ them as two separate components. As will be later described, the present invention combines the ferroelectric phase shifter and antenna patches into one integrated module. This reduces the number of parts used, reduces the overall size of the array, cuts down on loss and simplifies the production of the antennas into a significantly more practical form.
Ferroelectric phase shift components require a DC voltage in order to cause a signal delay in an Rf signal. This necessitates a DC feed line that is independent of but controls the functioning of the antenna array. Prior art DC feed lines are positioned on the RF transmission line leading to the ferroelectric components. In order to keep the Rf signal, which should flow through the transmission line to the antenna patch, from traveling into the DC feed line, a resistor is used between the DC and Rf lines. Also, a capacitor is placed on both sides of the ferroelectric phase shift component to keep the DC voltage from destroying other associated system components. Both the resistor and the two capacitors contribute to loss, and are excess parts. As will be later described, and in accordance with the invention, DC voltage is fed directly into the patch at the node of an unused resonant mode, thus eliminating the need for a chip resistor and a chip capacitor.
Prior ferroelectric antennas require complicated impedance matching, for example, a standard Rf transmission line is 50 ohms. The ferroelectric component is usually around 2-5 ohms, depending on its ferroelectric composition. In prior designs, the phase shifter had impedance matching tabs on both sides of the ferroelectric component to match from 50 ohms to 4 ohms at one end and back to 50 ohms at the other end. The antenna was also matched to 50 ohms by using cutaways in the patches. This design is redundant because it requires two impedance matching changes between the ferroelectric component and the patch. It would be more efficient to simply match the ferroelectric component at 2-5 ohms directly to the patch. This would reduce complexity and, importantly, it would save space. As will be later shown, and in accordance with an important feature of the invention, the Rf feed is impedance matched directly to the side or edge of the antenna patch. Thus, instead of bringing the Rf feed line closer to the center of the resonating length by cutting out an inset in the center of the patch, the feed can simply be brought to a desired location on the edge of the antenna patch suitable for direct matching to the ferroelectric component.